High performance heat pump unit

ABSTRACT

A heat pump unit ( 1 ) comprises at least one main circuit ( 2 ) adapted to perform a main heat pump cycle with a respective operating fluid, which comprises: a main condenser (S 4 ) adapted to perform the condensation of the operating fluid of the main heat pump cycle and intended to be connected to an external circuit of a first thermal user plant ( 10 ) in a heating operating mode of said heat pump unit ( 1 ), a first heat exchanger (S 2 ), connected downstream of the main condenser (S 4 ) and upstream of expansion means (L 2 ) of said the main circuit ( 2 ), adapted to perform an undercooling of the operating fluid of the main heat pump cycle after the condensation of the same in the main condenser (S 4 ), and a main evaporator (S 8 ) adapted to perform the evaporation of the operating fluid of the main heat pump cycle and intended to be connected to an external circuit of a heat sink ( 20 ) in a heating operating mode of said heat pump unit ( 1 ). The heat pump unit ( 1 ) further comprises a secondary circuit ( 3 ) adapted to perform a secondary heat pump cycle with a respective operating fluid, which comprises: a secondary evaporator (S 2 ) adapted to perform at least the evaporation of the operating fluid of the secondary heat pump cycle and in heat exchange relationship with the first heat exchanger (S 2 ) to transfer heat power released by the operating fluid of the main heat pump cycle during said undercooling to the operating fluid of the secondary heat pump cycle, and a secondary condenser (S 1 ) adapted to perform the condensation of the operating fluid of said secondary heat pump cycle (HPCS) and intended to be connected to the external circuit of the first thermal user plant ( 10 ) or to an external circuit of a second thermal user plant, different from the first thermal user plant ( 10 ).

FIELD OF THE INVENTION

The present invention relates to the field of heat pumps. In particular,the invention relates to a heat pump unit adapted to be used forheating/cooling environments and for producing sanitary hot water withhigh performance in terms of energy efficiency and use flexibility.

PRIOR ART

Heat pumps are an increasingly widespread technical solution for meetingthe requirements of heating/cooling environments and/or fluids. Thereasons for such a success are mainly to be ascribed to the high energyefficiencies, to the possibility of using a single device for bothheating and cooling (so-called “reversible” heat pumps), to theflexibility in managing thermal users with different requirements and tothe possibility, in case of use for heating, of considerably reducingthe use of fossil fuels and thus the output of harmful carbon harmful tothe environment.

In order to make the use of heat pumps increasingly competitive, thefocus of designers and manufacturers is on a constant improvement of theperformance thereof, both in terms of energy efficiency and in terms ofuse flexibility (possibility of use for both heating and cooling,possibility of meeting multiple different requirements of multiplethermal users, even concurrently, in terms of heating/cooling powerand/or operating temperatures, capability of operating at partial loadswithout energy efficiency degradation, etc.). The optimization need isespecially felt for heat pump units having a high heating/cooling power(for example >100 kW), typically intended to be used in large buildingswith centralized thermal users, such as blocks of flats, hotels,hospitals, barracks, sports centers, swimming pools, etc.

In the case of gas compression heat pumps a intended for heating, aknown method for improving the COP (Coefficient of Performance) consistsin performing an undercooling of the operating fluid after thecondensation thereof and in using the undercooling heat power thusobtained for preheating the heat carrier fluid coming from a heat sinkbefore sending it to the evaporator for determining the evaporation ofthe operating fluid.

Documents DE 3311505 A1 and WO 2011/045752 A1 describe the use to theabove solution in particular in so-called “high temperature” gascompression heat pumps. Such heat pumps allow condensation temperaturesof 80-85° C. to be achieved—required for the operation of conventionalhigh temperature heating plants which typically require a deliverytemperature of the heat carrier fluid of at least 80° C.—even when aheat sink is provided, the average temperature thereof does not exceed7-10° C., as it normally happens with groundwater. Two stage heat pumpsare typically needed in order to operate with so large differences,which however usually have relatively low COP.

In two stage heat pumps described in the above documents there isprovided an additional heat exchanger connected downstream of thecondenser and upstream of the expansion means in the circuit of eachstage. The additional heat exchangers are further connected to adelivery line of a heat carrier fluid of a heat sink, upstream of theevaporator of the lower temperature stage. Therefore, the heat carrierfluid coming from the heat sink can be preheated before sending it tothe evaporator of the lower temperature heat pump cycle through the heatpower resulting from the undercooling of the operating fluids thatperform the higher and lower temperature heat pump cycles. Due to such aconfiguration, COP can be obtained so as to be equal to or higher than 3even in two stage heat pumps.

SUMMARY OF THE INVENTION

The technical problem at the basis of the present invention consists inproviding a heat pump having improved performance as compared to theheat pumps having the same power and type of the prior art. Inparticular, a heat pump is desired which is capable of ensuring a highenergy efficiency, with COP in case of heating or EER (Energy EfficiencyRatio) in case of cooling equal to or higher than 3, in a wide range ofoperating conditions, also in the presence of thermal users withdifferent requirements in terms of heating/cooling power and/oroperating temperatures required.

The Applicants have perceived the possibility of solving such atechnical problem using the heat power resulting from an undercoolingsubsequent to the condensation of the operating fluid in a heat pumpcycle in an alternative and more effective manner with respect to thesolution presented in the prior art described above.

The invention therefore relates to a heat pump unit comprising at leastone main circuit adapted to perform a main heat pump cycle with arespective operating fluid, said at least one main circuit comprising:

-   -   a main condenser adapted to perform the condensation of the        operating fluid of said main heat pump cycle and intended to be        connected to an external circuit of a first thermal user plant        in a heating operating mode of said heat pump unit;    -   a first heat exchanger, connected downstream of said main        condenser and upstream of expansion means of said at least one        main circuit, adapted to perform an undercooling of the        operating fluid of said main heat pump cycle after the        condensation of the same in said main condenser, and    -   a main evaporator adapted to perform the evaporation of the        operating fluid of said main heat pump cycle and intended to be        connected to an external circuit of a heat sink in a heating        operating mode of said heat pump unit,        characterized by comprising a secondary circuit adapted to        perform a secondary heat pump cycle with a respective operating        fluid, said secondary circuit comprising:    -   a secondary evaporator adapted to perform at least the        evaporation of the operating fluid of said secondary heat pump        cycle and in heat exchange relationship with said first heat        exchanger to transfer heat power released by the operating fluid        of said main heat pump cycle during said undercooling to the        operating fluid of said secondary heat pump cycle, and    -   a secondary condenser adapted to perform the condensation of the        operating fluid of said secondary heat pump cycle and intended        to be connected to the external circuit of said first thermal        user plant or to an external circuit of a second thermal user        plant, different from said first thermal user plant.

Within the scope of the present description and in the following claims

-   -   the expression “heat pump cycle” is understood to indicate a        generic inverted thermodynamic cycle, i.e. a thermodynamic cycle        adapted to transfer heat power from a means or system at lower        temperature to a means or system at higher temperature, or in        order to increase or keep the temperature of the means or system        at higher temperature high (heating operation), or in order to        decrease or keep the temperature of the means or system at lower        temperature low (cooling operation), and    -   the expression “heat sink” is understood to indicate a means or        system capable of yielding or absorbing heat power without        considerable variations of the average temperature thereof.

In the heat pump unit of the invention, due to the performance of asecondary heat pump cycle with the above features, the heat powerreleased during the undercooling of the operating fluid of the main heatpump cycle can be advantageously brought substantially to the sametemperature at which the condensation heat power in the main condenseris released. Thereby, also the undercooling heat power of the mainoperating fluid may be transferred to the thermal user plant served bythe main heat pump cycle or to another thermal user plant operating atsimilar temperatures, increasing the overall useful heat power that canbe provided by the heat pump unit.

The Applicants have surprisingly found that, unlike what happens forexample in the case of the cascading coupling of two heat pump cyclesaccording to the prior art, in this case the increase of the aboveuseful heat power leads to an improvement of the overall COP. This isessentially related to the fact that such an increase in the useful heatpower may be achieved with a minimum additional use of energy, inparticular electrical energy for compressing the operating fluid in thesecondary heat pump cycle. It has been determined that with a suitableselection of the operating fluids and of the operating parameters, anincrease in the COP up to 20% can be advantageously obtained as comparedto the values obtainable in conventional heat pumps of the same type andpower.

In fact, it should be noted that the undercooling of the operating fluidof the main heat pump cycle takes place, due to its nature, with atemperature variation. The heat power released during the undercoolingof the operating fluid of the main heat pump cycle therefore allows notonly the evaporation but also a strong overheating of the operatingfluid of the secondary heat pump cycle, to be obtained.

The overheating degree obtainable on the operating fluid of thesecondary heat pump cycle, which is stronger as the thermal gradient ofthe operating fluid of the main heat pump cycle is wider during theundercooling, has two important effects that contribute to aconsiderable reduction of the electrical compression power in thesecondary heat pump cycle.

In the first place, there occurs an increase in the enthalpy jumpundergone by the operating fluid of the secondary heat pump cycle in theheat exchange with the main operating fluid in the undercooling step.Having established the heat power to transfer between the two fluids,such an enthalpy jump allows a corresponding reduction in the mass flowrate of the operating fluid of the secondary heat pump cycle so thatless compression work is required.

In the second place, the overheating distances the operating fluid ofthe secondary heat pump cycle from the saturation conditions andtherefore allows the use of compressors with higher isentropic yields,without the risk of intersecting the higher limit curve (i.e. saturationcurve in vapor conditions) during the compression.

Both aspects mentioned contribute to a reduction in the electrical powerused for the compression of the operating fluid of the secondary heatpump cycle and thus, according to what explained above, to the increasein the overall COP of the heat pump unit of the invention.

The heat pump unit of the invention with the above features, moreover,provides a considerable use flexibility. In fact, if no additional heatpower at the higher temperature is required, or in case of coolingoperation when this option is provided, the secondary heat pump cyclecan be easily deactivated and the heat power resulting from theundercooling of the main operating fluid can be released to the externalenvironment or used for other purposes.

To this end, it should also be noted that the use of the secondary heatpump cycle in the heat pump unit of the invention is compatible andeasily integrated with other technical solutions aimed to use theundercooling heat power of the main operating fluid, such as for examplethe preheating of the heat carrier fluid of the heat sink carried out inthe prior art devices.

In a preferred embodiment of the heat pump unit of the invention, bothsaid main condenser and said secondary condenser are intended to beconnected to the external circuit of said first thermal user plant andare connected to one another so as to be in series in said externalcircuit of said first thermal user plant.

This embodiment advantageously allows the use of both the condensationheat power and of the undercooling heat power of the main operatingfluid for the same thermal user plant.

A situation of interest for the use of this embodiment therefore is incombination with high temperature heating plants which envision hightemperature differences between delivery and backflow of the respectiveheat carrier fluid.

Advantageously, moreover, due to the possibility of performing theheating of the heat carrier fluid of the thermal user plant in two stepsthat occur in a sequence in the secondary condenser and in the maincondenser, with this embodiment it is possible to further improve theoverall COP of the heat pump unit. In fact, since in this case thesecondary condenser must only contribute to a part of the heating, theheat power to transfer to the thermal user plant being equal, it ispossible to decrease the condensation temperature in the secondary heatpump cycle, obtaining a simultaneous decrease of the compression workrequired in such a cycle and in the practice, an increase in the overallCOP of the heat pump unit.

In another preferred embodiment, said main circuit comprises a firstsub-circuit adapted to perform a higher temperature main heat pump cyclewith a respective operating fluid and a second sub-circuit adapted toperform a lower temperature main heat pump cycle with a respectiveoperating fluid, in which said first and second sub-circuits are incascading heat exchange relationship with each other to perform globallya two-stage main heat pump cycle, and in which said main condenser andsaid first heat exchanger are connected in said first sub-circuit andsaid main evaporator is connected in said second sub-circuit.

Such a configuration of the main circuit allows a two-stage main heatpump cycle to be performed, and thus the operation with thermalgradients significantly higher than those obtainable through asingle-stage heat pump cycle. Due to this, the heat pump unit of theinvention can be advantageously used with thermal user plants operatingat a high temperature (for example radiator heating plants whichnormally require delivery temperatures around 80° C.) also when a heatsink is available which consists of water or environmental fluids at lowtemperature (for example groundwater or running water on the surface orin depth, seawater or lake water, waterworks water, wastewaters, etc.,with average temperatures typically not lower than about 7° C.).

Preferably, said first sub-circuit comprises a second heat exchangerconnected downstream of said first heat exchanger and upstream ofexpansion means of said first sub-circuit, said second heat exchangerbeing adapted to perform an undercooling of the operating fluid of saidhigher temperature main heat pump cycle after the condensation thereofand being selectively connectable to the external circuit of said heatsink so as to perform a preheating of a heat carrier fluid coming fromsaid heat sink by means of heat power released during said undercoolingby the operating fluid of said higher temperature main heat pump cycle.

The recovery of heat power resulting from the undercooling of theoperating fluid of the higher temperature main heat pump cycle forpreheating the heat carrier fluid of the heat sink when the heat pumpunit of the invention is active in heating implies a further improvementof the overall COP.

Preferably, said second heat exchanger is further selectivelyconnectable to an external circuit of a third thermal user plant.

Thereby, the heat power resulting from the undercooling of the operatingfluid of the higher temperature main heat pump cycle may be used forserving a further medium/low temperature thermal user, for example aheating plant with floor or ceiling radiating panels, fan coils, etc.The possibilities of use and the overall energy efficiency of the heatpump unit of the invention therefore are advantageously increased.

Preferably, said second sub-circuit comprises a third heat exchangerconnected downstream of said first heat exchanger and upstream ofexpansion means of said second sub-circuit, said third heat exchangerbeing adapted to perform an undercooling of the operating fluid of saidlower temperature main heat pump cycle after the condensation thereofand being selectively connectable to the external circuit of said heatsink so as to perform, preferably independently of said second heatexchanger, a preheating of a heat carrier fluid coming from said heatsink by means of heat power released during said undercooling by theoperating fluid of said lower temperature main heat pump cycle.

Preferably, said third heat exchanger is further selectively connectableto the external circuit of said third thermal user plant.

These embodiments replicate, in the second sub-circuit for performingthe lower temperature main heat pump cycle, what described above withreference to the first sub-circuit for performing the higher temperaturemain heat pump cycle, advantageously allowing the increase of the heatpower available for preheating the heat carrier fluid of the heat sinkor a medium/low temperature thermal user to be served.

In a preferred embodiment, said first sub-circuit comprises a fourthheat exchanger connected downstream of said main condenser and upstreamof said first heat exchanger, said fourth heat exchanger being adaptedto perform an undercooling of the operating fluid of said highertemperature main heat pump cycle after the condensation of the same andbeing selectively connectable to the external circuit of said firstthermal user plant so as to be in series with said main condenser insaid external circuit of said first user plant.

This embodiment advantageously allows the use of heat power resultingfrom an undercooling of the operating fluid of the main heat pump cycle(i.e. of the higher temperature main heat pump cycle in the case oftwo-stage main heat pump cycle) for preheating the heat carrier fluid ofthe first thermal user plant before it reaches the main condenser, witha positive effect on the overall COP of the heat pump unit.

It should be noted that the advantages on the COP obtainable by thissolution are related to the undercooling heat power fraction actuallyusable with respect to the theoretically available one, which isdetermined by the minimum temperature achievable with the undercooling,i.e. the evaporation temperature of the operating fluid of the main heatpump cycle (or of the higher temperature main heat pump cycle).

Since the undercooling heat power usable is greater as the backflowtemperature of the heat carrier fluid to be heated is lower, the aboveembodiment is especially advantageous for an operation of the heat pumpunit in all those operating conditions in which a drop of thetemperature level in the thermal user plant is acceptable with the sameheat power transferred thereto. Such a situation occurs, for example, inhigh temperature heating plants in autumn and spring.

In general, therefore, this embodiment finds an advantageous use incombination with high temperature heating plants which provide for thepossibility of changing the backflow temperature of the heat carrierfluid in order to optimize the operation of the heating plant.

Preferably, the heat pump unit according to the invention comprisesswitching means, adapted to allow an exchange of connections of theexternal circuits of at least said first thermal user plant and saidheat sink respectively with at least said main condenser and with saidmain evaporator.

This allows a reversible heat pump unit to be obtained, capable ofoperating both for heating and for cooling. Advantageously, the choiceto perform the cycle reversal by exchanging the external circuits of thethermal user(s) and of the heat sink, respectively, releases theswitching between the two operating modes from the specificconfiguration of the heat pump unit (main circuit with one or twostages, number of heat exchangers connected to a same delivery line ofthe thermal user plant(s), etc.).

Preferably, the operating fluid of said main heat pump cycle, or theoperating fluids of said higher temperature main heat pump cycle andsaid lower temperature main heat pump cycle respectively, and theoperating fluid of said secondary heat pump cycle are selected from thegroup consisting of: (E)-2-butene, (Z)-2-butene, 1-butylene, dimethylketone, methylacetylene, methyl alcohol, methylpentane, methylpropene,n-hexane, R1270, R290, R600, R600a, R601, R601a, RE-170,tetramethylmethane or RC-270.

The above cooling fluids are characterized by limit curves in diagramh-p (specific enthalpy—pressure) strongly inclined towards theincreasing enthalpies, with increasing inclination as pressureincreases. This advantageously allows even strong undercooling to beperformed which, as already explained, allows all the advantageouseffects on the overall energy efficiency that can be obtained by theabove embodiments of the heat pump unit to be enhanced.

The invention also relates to a system for heating/cooling environmentsand/or for producing sanitary hot water comprising a heat pump unithaving the features described above

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the present invention will appearmore clearly from the following description of some preferredembodiments thereof, made by way of a non-limiting example withreference to the annexed drawings, in which:

FIG. 1 shows a circuit diagram of a first preferred embodiment of theheat pump unit of the invention;

FIG. 1A schematically shows a diagram h-p of the heat pump cyclesperformed in the heat pump unit of the invention in the embodiment inFIG. 1;

FIG. 2 shows a circuit diagram of a second preferred embodiment of theheat pump unit of the invention;

FIG. 2A schematically shows a diagram h-p of the heat pump cyclesperformed in the heat pump unit of the invention in the embodiment inFIG. 2;

FIG. 3 shows a circuit diagram of a variant of the embodiment in FIG. 2;

FIG. 4 shows a circuit diagram of a third preferred embodiment of theheat pump unit of the invention;

FIG. 5 shows a circuit diagram of a fourth preferred embodiment of theheat pump unit of the invention;

FIG. 6 shows a circuit diagram of a fifth preferred embodiment of theheat pump unit of the invention;

FIGS. 7A and 7B show circuit diagrams of two operating configurations ofa sixth preferred embodiment of the heat pump unit of the invention;

FIGS. 8A and 8B show circuit diagrams of two operating configurations ofa seventh preferred embodiment of the heat pump unit of the invention;

FIGS. 9A and 9B show circuit diagrams of two operating configurations ofan eighth preferred embodiment of the heat pump unit of the invention;

FIGS. 10A and 10B show circuit diagrams of two operating configurationsof an ninth preferred embodiment of the heat pump unit of the invention,and

FIG. 11 shows a circuit diagram of a tenth preferred embodiment of theheat pump unit of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the figures, a heat pump unit according to the invention is globallyindicated with reference numeral 1.

In such figures, the heat pump unit 1 is shown as a part of a system 100for heating/cooling environments and/or for producing sanitary hotwater, comprising at least one external circuit of a thermal user plant10 and an external circuit of a heat sink 20, which are onlyschematically shown.

In situations of use of the heat pump unit 1 in which both heatproduction and cold production are concurrently required, the heat sink20 may therefore be replaced by a further thermal user plant capable ofusing the cooling or heating power otherwise disposed of through such aheat sink.

FIG. 1 shows a first preferred embodiment of the heat pump unit 1, inparticular for heating, comprising a main circuit 2 and a secondarycircuit 3 adapted to perform respective heat pump cycles in heatexchange relationship with each other, with respective operating fluids.

The main circuit 2 for performing a main heat pump cycle HPCM comprises:a main condenser S4 adapted to perform the condensation of the operatingfluid at a higher pressure of the main heat pump cycle HPCM and intendedto be connected to the external circuit of the thermal user plant 10 ina heating operating mode of the heat pump unit 1; a main evaporator S8adapted to perform the evaporation of the operating fluid at a lowerpressure of the main heat pump cycle HPCM and intended to be connectedto the external circuit of the heat sink 20 in a heating operating modeof the heat pump unit 1; a compressor C2 adapted to bring the evaporatedoperating fluid from the lower pressure to the higher pressure of themain heat pump cycle HPCM, and expansion means L2—for example alamination valve or other functionally equivalent known device—adaptedto perform the expansion of the operating fluid from the higher pressureto the lower pressure of the main heat pump cycle HPCM.

The main circuit 2 further comprises a heat exchanger connecteddownstream of the main condenser S4 and upstream of the expansion meansL2, adapted to perform an undercooling of the operating fluid after thecondensation of the same in the main condenser S4 and in heat exchangerelationship with the secondary circuit 3.

Within the scope of the present description and of the following claims,the expressions “upstream” and “downstream” are to be understood withreference to the directions of fluid circulation indicated in thefigures by arrows and in general determined by the compressors, in thecase of circuits for performing heat pump cycles, and by the circulationpumps in the case of the external circuits of the thermal user plantsand of the heat sink, respectively.

Likewise, the secondary circuit 3 for performing a secondary heat pumpcycle HPCS comprises: a secondary condenser S1 adapted to perform thecondensation of the operating fluid at a higher pressure of thesecondary heat pump cycle HPCS and intended to be connected to theexternal circuit of the thermal user plant 10 or to the external circuitof another separate thermal user plant (see thermal user plant 11 inFIG. 3); a secondary evaporator adapted to perform at least theevaporation of the operating fluid at a lower pressure of the secondaryheat pump cycle HPCS and in heat exchange relationship with said heatexchanger of the main circuit 2 for transferring heat power released bythe operating fluid of the main heat pump cycle HPCM during saidundercooling to the operating fluid of the secondary heat pump cycleHPCS; a compressor C3 adapted to bring the evaporated operating fluidfrom the lower pressure to the higher pressure of the secondary heatpump cycle HPCS, and expansion means L3—for example a lamination valveor another functionally equivalent known device—adapted to allow theexpansion of the operating fluid from the higher pressure to the lowerpressure of the secondary heat pump cycle HPCS.

In the preferred embodiments shown in the figures, said heat exchangerof the main circuit 2 and the secondary evaporator of the secondarycircuit 3 are integrated in a single heat exchanger device S2 forgreater construction compactness and a better heat exchange efficiency.In any case, embodiments in which such components are separate andplaced in thermal exchange relationship by an intermediate circuit forthe circulation of a suitable heat carrier fluid are not excluded.

Compressor C3 preferably is a variable flow rate compressor, for examplea cut-off or step or inverter compressor. This allows the extent of theoperating fluid undercooling in the main heat pump cycle HPCM at theheat exchanger device S2 and accordingly, the heat power that can beprovided at the secondary condenser S1 to be controlled withoutstressing the compressor with an excessive repetition of on-off cycles.

Through the secondary circuit 3 and the related secondary heat pumpcycle HPCS described above, it is possible to raise the temperaturelevel of the heat power released upon the undercooling of the operatingfluid in the main heat pump cycle HPCM, thus making also such a heatpower usable by the thermal user plant 10 or by another and separatethermal user plant operating at medium or high temperature. Due to thefact that such a result may be obtained minimizing the additional energyconsumption related to compressor C3, as already explained above, theincrease in the useful heat power leads to an increase in the overallCOP of the heat pump unit 1.

FIG. 1A schematically shows a diagram h-p (specific enthalpy-pressure)of the main HPCM and secondary HPCS heat pump cycles that may beperformed in the heat pump unit 1 in FIG. 1.

In particular, it can be seen that in the main heat pump cycle HPCM,after condensation C′-D′ performed in the main condenser S4, theoperating fluid undergoes an undercooling D′-E′, performed in the heatexchanger device S2. Through the heat exchanger device S2, the heatpower released during the undercooling D′-E′ is transferred to thesecondary heat pump cycle HPCS. Such a heat power is used for performingevaporation A″-F″ of the operating fluid of the secondary heat pumpcycle HPCS and also a substantial overheating F″-B″ of the same. Asalready explained above, the possibility of performing such a highoverheating has advantageous effects on the secondary heat pump cycleHPCS, which in turn lead to an improvement in the overall COP of theheat pump unit 1. The heat powers released during the condensation stepC′-D′ in the main heat pump cycle HPCM at the main condenser S4 andduring the condensation step C″-D″ in the secondary heat pump cycle HPCSat the secondary condenser S1, respectively, as said, may both betransferred to the same thermal user plant or to two separate thermaluser plants.

As shown in FIG. 1, when both the main condenser S4 and the secondarycondenser S1 are intended to serve the same thermal user plant, they arereciprocally connected in series, with the secondary condenser S1upstream, in a line FL1 arranged in the heat pump unit 1 for theconnection to the external circuit of such a thermal user plant.Thereby, the secondary condenser S1 can be used for performing apreheating of the heat carrier fluid of the thermal user plant, and themain condenser S4 for completing the heating up to reaching the requireddelivery temperature.

As already explained above, since in this case the secondary condenserS1 must only contribute to a part of the heating, the heat power totransfer to the thermal user plant being equal, it is possible todecrease the condensation temperature in the secondary heat pump cycleHPCS, obtaining a simultaneous decrease of the compression work requiredin such a cycle and thus, a further improvement of the overall COP ofthe heat pump unit 1.

According to the minimum temperature of the heat sink 20 available, theembodiment of the heat pump unit 1 shown in FIG. 1 may be used withlow/mean or high temperature thermal user plants.

For example, if a heat sink 20 is available with a mean temperature ofno less than 7° C., as it happens for example in the case of groundwateror running water on the surface or in depth, seawater or lake water,waterworks water, wastewaters, etc., it is possible to serve thermaluser plants that require temperatures up to 60-65° C., for exampleheating plants operating at low/mean temperature, such as plants withfloor or ceiling radiating panels, fan coils, etc., or plants for theproduction of sanitary hot water.

On the other hand, if a heat sink 20 is available with a higher meantemperature (at least 30-35° C.), for example waste/cooling heat fromindustrial processes, hot spring, etc., it is possible to serve thermaluser plants which require temperatures even higher than 60-65° C., forexample heating plants operating at high temperature, such as plantswith radiators, fan heaters, etc. which typically require deliverytemperatures of 80° C. or higher, or plants for the production ofsanitary hot water in all those situations where the hot water must beproduced at temperatures considerably higher than 60° to prevent thepossible occurrence of legionella (hospitals, swimming pools and sportscenters, barracks, etc.).

The Applicant has therefore noted that through the heat pump unitaccording to the invention, the “useless” enthalpy of the operatingfluid is advantageously changed into “useful” enthalpy. Through a strongundercooling of the operating fluid of the main circuit 2, the sameoperating fluid at the output from compressor C2 has an overall enthalpygiven by the sum of a “useful” enthalpy, obtainable by thede-overheating followed by the condensation of the operating fluidthrough the main condenser S4, and by the “useful” enthalpy obtainableby the undercooling of the operating fluid through the first heatexchanger S2. The term “useful” indicates the possibility oftransferring high temperature heat power (i.e. at temperatures close tothose of condensation) to a heat carrier fluid, whereas the term“useless” indicates the possibility of transferring heat power only attemperatures strongly lower than those of condensation. According to thepresent invention, the “useless” enthalpy is used to evaporate anoperating fluid circulating in the secondary cycle HPSC which, by meansof a secondary compressor C3, is able to condensate at a temperaturecorresponding to the useful enthalpy. In order to obtain this result,the operating fluid circulating in the main circuit is stronglyundercooled, i.e. so as to bring the same fluid from an initialtemperature close to the condensation temperature up to a temperatureclose to the evaporation one. FIG. 2 shows a second preferred embodimentof the heat pump unit 1, which differs from that in FIG. 1 in the typeof main circuit 2. In this case, the main circuit 2 comprises a firstsub-circuit 2 a adapted to perform a higher temperature main heat pumpcycle HPCM_HT with a respective operating fluid and a second sub-circuit2 b adapted to perform a lower temperature main heat pump cycle HPCM_LTwith a respective operating fluid. The first and second sub-circuits 2a, 2 b are in cascading heat exchange relationship with each other toperform globally a two-stage main heat pump cycle HPCM.

In this case, the first sub-circuit 2 a comprises the main condenser S4,the heat exchanger device S2, the expansion means L2 and compressor C2described above with reference to the embodiment in FIG. 1, and anevaporator. The second sub-circuit 2 b comprises the main evaporator S8,already described above as well with reference to the embodiment in FIG.1, a compressor C1, a condenser in heat exchange relationship with theevaporator of the first sub-circuit 2 b and the expansion means L1.

In the preferred embodiments shown herein, the condenser of the secondsub-circuit 2 b and the evaporator of the first sub-circuit 2 a areintegrated in a single heat exchanger device S7 for greater constructioncompactness and a better heat exchange efficiency. In any case,embodiments where such components are separate and placed in thermalexchange relationship by an intermediate circuit for the circulation ofa suitable heat carrier fluid are not excluded.

The embodiment of the heat pump unit 1 with two-stage main heat pumpcycle HPCM finds an advantageous use in all those situations in which itis necessary to serve thermal user plants operating at a hightemperature but having a low temperature heat sink available.

FIG. 2A schematically shows a diagram h-p of the main HPCM and secondaryHPCS heat pump cycles that may be performed in the heat pump unit 1 inFIG. 2. In this case, the main heat pump cycle HPCM consists of the twomain heat pump cycles at higher temperature HPCM_HT and at lowertemperature HPCM_LT, respectively, in cascading heat exchangerelationship with each other. In particular, through the heat exchangerdevice S7, the heat power released during condensation C-D of theoperating fluid of the lower temperature main heat pump cycle HPCM_LT istransferred to the operating fluid of the higher temperature main heatpump cycle HPCM_HT for performing the evaporation (and optionaloverheating) A′-B′ thereof.

The relationship between the higher temperature main heat pump cycleHPCM_HT and the secondary heat pump cycle HPCS is totally similar tothat already described with reference to the diagram in FIG. 1A.

As indicated above, it has been seen that through the heat pump unitaccording to the invention, the “useless” enthalpy resulting from theundercooling of the operating fluid is advantageously converted intoenthalpy useful for heating the heat carrier fluid of the externalcircuit of the first user plant 10. Considering for example a“cascading” cycle like that in FIG. 2, where Isobutane -R600 is used asoperating fluid for the main circuit 2 and for the secondary one 3, ithas been seen that against the 34 KW required for the operation ofcompressors C1, C2 of sub-circuits 2 a and 2 b, the operating fluid ofthe main circuit has an enthalpy useful for the main condenser S4capable of transferring a power of 100 thermal KW at 80° C. to the heatcarrier fluid of the external circuit. The same operating fluid also hasan enthalpy “useless” for the first heat exchanger S2 capable oftransferring a heat power of 38 thermal KW at 40° C. to evaporator S1 ofthe secondary cycle 3. Compressor C3 of the secondary cycle 3, againstthe 8 electrical KW used, is capable of transferring an additional heatpower of 46 thermal KW at 80° C. to the heat carrier fluid circulatingin the external circuit that adds up to the 100 thermal KW of enthalpyuseful for the main exchanger S4 of the main circuit 2. Overall, it hastherefore been seen that the heat carrier fluid receives 146 thermal KWat 80° C. against a use of 42 KW.

In order to provide the same 146 thermal KW at 80° C. to the heatcarrier fluid without making the “useless” enthalpy “useful”, the optionmay be to increase the mass flows rate of the operating fluids relatedto the dual cascading cycle by 46%. However, thereby, the electricalpower used by the compressors would increase proportionally and the COPwould remain unchanged (equal to 2.94). Moreover, thereby it would benecessary to also increase the flow rate of cold fluid to the evaporatorof the second sub-circuit 2 b by 46%. On the other hand, the heat pumpunit allows 46% of the electrical power used and 46% of the flow rate ofcold fluid to the evaporator of the second sub-circuit 2 b to be saved,the yielded heat power at 80° C. being the same.

FIG. 3 shows a variant of the embodiment in FIG. 2, in which the maincondenser S4 and the secondary condenser S1 are intended to be connectedto external circuits of two separate thermal user plants 10, 11. Thisvariant, which may be implemented in a similar manner also inembodiments of the heat pump unit 1 with single-stage main heat pumpcycle HPCM (FIG. 1), is advantageous in all those situations in which itis necessary to serve two medium/high temperature thermal user plantshaving different operating requirements (different operatingtemperatures, different operating periods, etc.).

FIG. 4 shows a third preferred embodiment of the heat pump unit 1 whichdiffers from that in FIG. 2 essentially by the provision, in the firstsub-circuit 2 a for performing the higher temperature main heat pumpcycle HPCM_H, of a further heat exchanger S5 connected downstream of theheat exchanger device S2 and upstream of the expansion means L2.

Heat exchanger S5 is adapted to perform an undercooling of the operatingfluid of the higher temperature main heat pump cycle HPCM_HT after thecondensation thereof in the main condenser S4, and optionally after afirst undercooling in the heat exchanger device S2, and is selectivelyconnectable to the external circuit of the heat sink 20 so as to performa preheating of the heat carrier fluid coming from the latter by meansof the heat power released during said undercooling.

In particular, a first end of the heat exchanger S5 is connected in thefirst sub-circuit 2 a as described above and a second end of the heatexchanger S5 is connected upstream of the main evaporator S8 in a lineFL2 arranged in the heat pump unit 1 for the connection to the externalcircuit of the heat sink 20. In such a line FL2 there is also provided avalve V7, preferably a modulating solenoid valve, for adjusting the flowrate of heat carrier fluid of the heat sink 20 which crosses the heatexchanger S5, and thus the extent of the undercooling of the operatingfluid in the higher temperature main heat pump cycle HPCM_HT. Line FL2preferably also comprises a first manifold M1 connected upstream of theheat exchanger S5 and a second manifold M2 connected upstream of themain evaporator S8 and downstream of valve V7. Preferably, manifolds M1and M2 are also connected by a bypass line BPL for bypassing the heatexchanger S5, provided with a valve V5, also preferably a modulatingsolenoid valve.

This further embodiment of the heat pump 1 therefore allows the heatpower obtained with the undercooling of the operating cycle of thehigher temperature main heat pump cycle HPCM_HT to be used forpreheating the heat carrier fluid of the heat sink 20, in addition or asan alternative to the use through the secondary heat pump cycle HPCSthat may be performed in the secondary circuit 3 described above.

In particular, when compressor C3 of the secondary circuit 3 is off, theundercooling is carried out only in heat exchanger S5. When compressorC3 is cut off or operates at a reduced number of revolutions, theundercooling is partly carried out in the heat exchanger device S2 andpartly in heat exchanger S5. In this case, valve V7 is correspondinglycut off. When compressor C3 operates at full load, preferably all theundercooling heat power available is used in the heat exchanger deviceS2 and heat exchanger S5 is disabled by closing valve V7. Preferably, inorder to keep a constant flow rate of the heat sink 20 heat carrierfluid in the main evaporator S8, a modulation or closure of valve V7 iscompensated through a corresponding modulation or opening of valve V5.Preferably, in this embodiment and in those described hereinafter,compressors C1 and C2 are variable flow rate compressors, for examplecut-off step or inverter compressors. This ensures higher adaptabilityof the heat pump unit 1 to the possible unbalances in the thermal powerexchange between higher temperature main heat pump cycle HPCM_HT andlower temperature main heat pump cycle HPCM_HT which may happen due tothe undercooling. Such a higher adaptability has a positive influence onthe overall energy efficiency of the heat pump unit 1, all the otherconditions being equal.

FIG. 5 shows a fourth preferred embodiment of the heat pump unit 1 whichdiffers from that in FIG. 4 by the provision, in the second sub-circuit2 b for performing the lower temperature main heat pump cycle HPCM_LT,of a further heat exchanger S6 connected downstream of the heatexchanger device S7 and upstream of the expansion means L1.

Similar to heat exchanger S5, heat exchanger S6 is adapted to perform anundercooling of the operating fluid of the lower temperature main heatpump cycle HPCM_LT after the condensation thereof in the heat exchangerdevice S7, and is selectively connectable to the external circuit of theheat sink 20 so as to perform a preheating of the heat carrier fluidcoming from the latter by means of the heat power released during saidundercooling.

Preferably, heat exchanger S5 and heat exchanger S6 are arranged so asto perform the preheating of the heat carrier fluid of the heat sink 20independently of one another, i.e. operating in parallel on two separateflows of such a heat carrier fluid.

In particular, as shown in FIG. 5, the heat exchanger S5 and valve V7are connected in a first branch FL2′ of line FL2 for the connection tothe external circuit of the heat sink 20 and heat exchanger S6 isconnected in a second branch FL2″, in parallel with the first branchFL2′, of line FL2. In such a line FL2″ there is also provided a valveV6, preferably a modulating solenoid valve, for adjusting the flow rateof heat carrier fluid of the heat sink 20 which crosses the heatexchanger S6. Similar to what mentioned with reference to valve V7, alsothe modulation or closing of valve V6 may be compensated through acorresponding intervention on valve V5 in the bypass line BPL in orderto keep a constant flow rate of the heat sink 20 heat carrier fluid inthe main evaporator S8.

This embodiment of the heat pump 1 allows an undercooling of theoperating fluid to be performed also in the lower temperature main heatpump cycle HPCM_LT after the condensation thereof and the heat powerthus released to be used for preheating the heat carrier fluid of theheat sink 20.

FIG. 6 shows a fifth preferred embodiment of the heat pump unit 1 whichdiffers from that in FIG. 5 in that the heat exchangers S5 and S6 arefurther selectively connectable to an external circuit of a furtherthermal user plant 12, in particular a thermal user plant operating atmean/low temperature, for example a heating plant with floor or ceilingradiating panels, a plant for the production of sanitary hot water, etc.

This is preferably obtained using a three-way valve V8, preferably asolenoid valve, and two valves V9 and V12, preferably modulatingsolenoid valves, arranged so as to allow the connection of the secondend of heat exchangers S5 and S6 alternately to the external circuit ofthe heat sink 20 or to the external circuit of the thermal user plant12.

In particular, when the heat power released at the heat exchangers S5and S6 must be used for serving the thermal user plant 12, the three-wayvalve V8 is diverted towards the external circuit of such a plant,valves V6 and V7 are fully closed and valves V9 and V12 are fully orpartly open. An adjustment of the opening degree of valves V9 and V12allows the heat power transferred to the thermal user plant 12 to beadjusted.

On the contrary, when the heat power released at the heat exchangers S5and S6 must be used for preheating the heat sink 20 heat carrier fluid,as in the embodiments described above with reference to FIGS. 4 and 5,the three-way valve V8 is diverted towards the external circuit of theheat sink, valves V9 and V12 are fully closed and valves V6 and V7 arefully or partly open.

In all the embodiments where the pairs of two-way valves V6+V9 andV7+V12 are provided, each of such pairs may be replaced by a three-wayvalve arranged so as to perform the functions described above of thecorresponding two-way valves.

FIGS. 7A and 7B show a sixth preferred embodiment of the heat pump unit1 adapted to operate for both heating and cooling, i.e. of thereversible type.

To this end, in this embodiment there are provided switching meansadapted to allow an exchange of connections of the external circuits ofthe thermal user plant 10 and of the heat sink 20 respectively with themain condenser S4 and with the main evaporator S8. Preferably, suchswitching means comprise two four-way valves V1 and V2, preferablysolenoid valves, suitably arranged in the lines for the connection ofthe above external circuits to the main condenser S4 and the mainevaporator S8.

In particular, in the operating configuration shown in FIG. 7A,corresponding to a heating operation (winter or autumn and spring), theexternal circuit of the thermal user plant 10 is connected to the maincondenser S4 (and to the secondary condenser S1), whereas the externalcircuit of the heat sink 20 is connected to the main evaporator S8 in amanner totally similar to the embodiments described above.

In the configuration shown in FIG. 7B, corresponding to a coolingoperation (summer), the external circuit of the thermal user plant 10 isconnected to the main evaporator S8 so as to provide such a plant withthe required cooling power whereas the external circuit of the heat sink20 is connected to the main condenser S8.

It is noted that in the cooling operation, the use of heat exchangers S5and S6 for the undercooling of the operating fluid respectively in thehigher temperature main heat pump cycle HPCM_HT and in the lowertemperature main heat pump cycle HPCM_LT allows a substantial increaseof the useful cooling power without a corresponding increase ofelectrical power used, to the advantage of the overall energyefficiency. Numerical simulations carried out have shown that thisembodiment of the heat pump unit 1 when operating for cooling allows EERvalues to be reached that are equal to 3.5-4.0, against a value of about2.2 in the absence of undercooling.

The undercooling heat power released in this operating configuration atthe heat exchangers S5 and S6 may advantageously be used for example forthe production of sanitary hot water in a dedicated plant (schematizedin FIG. 7B by the thermal user plant 12). If the undercooling heat powercannot be used, this shall be suitably disposed to the externalenvironment.

In case of cooling operation, the secondary circuit 3 for performing thesecondary heat pump cycle HPCS typically is not active (compressor C3off). Alternatively, for example in use situations in which theproduction of large amounts of sanitary hot water is required even inhot seasons, it is possible to provide also for the transfer of thepower released at the secondary condenser S1 to a plant for theproduction of sanitary hot water.

FIGS. 8A and 8B show a seventh preferred embodiment of the heat pumpunit 1 which differs from that of FIGS. 7A and 7B in that it can alsoserve, in a dedicated manner, both in a heating operating configuration(FIG. 8A), and in a cooling operating configuration (FIG. 8B), a thermaluser plant 13 for the production of sanitary hot water, in addition tothe thermal user plants 10 and 12 and optionally 11, already mentioned.This embodiment in particular allows a thermal user plant for theproduction of high temperature (higher than 60° C. to prevent thepossible occurrence of legionella) sanitary hot water to be served.

The embodiment shown in FIGS. 8A and 8B, by way of an example, envisionsthat the heat exchange with the thermal user plant 13 indirectly takesplace at a heat accumulator (boiler) 13 a, but other solutions known bythe man skilled in the art are also possible for connecting the heatpump unit 1 to the external circuit of such a thermal user plant.

With respect to the embodiment of FIGS. 7A and 7B, connections arefurther provided in this case for an external circuit of the thermaluser plant 13 and two three-way valves V3 and V11, preferably solenoidvalves.

The three-way valve V3 is arranged so as to allow, in the heatingoperating configuration (FIG. 8A), the connection of line FL1, in whichthe main condenser S4 and the secondary condenser S1 are connected,alternately to the external circuit of the thermal user plant 10 or tothe external circuit of the thermal user plant 13. Thereby, the heatpower released at the main condenser S4 (and at the secondary condenserS1 when the secondary circuit 3 is active) can be alternately used forheating or producing high temperature sanitary hot water.

The three-way valve V11 is arranged so as to allow, in the coolingoperating configuration (FIG. 8B), the connection of line FL1alternately to the external circuit of the thermal user plant 13.Thereby, the heat power released by the main condenser S4 (and of thesecondary condenser S1 when the secondary circuit 3 is active, acondition which may also occur during the cooling operation to meet ahigh hot water requirement) can be used for producing high temperaturesanitary hot water rather than dispersing such a power at the heat sink20.

FIGS. 9A and 9B show an eighth preferred embodiment of the heat pumpunit 1 which, as compared to the embodiment of FIGS. 8A and 8B, inaddition allows also low temperature sanitary hot water requirements tobe met through the thermal user plant 13 for the production of sanitaryhot water already mentioned. The embodiment of FIGS. 9A and 9B differsfrom that of FIGS. 8A and 8B in particular by the presence of a furtherthree-way valve V4, preferably a solenoid valve.

The three-way valve V4 is arranged so as to allow the selectiveconnection of lines FL2′ and FL2″, in which the heat exchangers S5 andS6 are connected, also to the external circuit of the thermal user plant13 for the production of sanitary hot water, so as to create a closedcircuit therewith. Thereby, the heat power released at the two heatexchangers S5 and S6 can be alternately used for producing sanitary hotwater both in the heating operating configuration (FIG. 9A) and in thecooling operating configuration (FIG. 9B), or for preheating the heatsink 20 heat carrier fluid in the heating operating configuration.

For an optimum operation of this embodiment in the cooling operatingconfiguration (FIG. 9B) it is suitable to provide, externally to theheat pump unit 10, means for bypassing the external circuit of thethermal user plant 10, intended for cooling in this operatingconfiguration. Such means preferably comprise a three-way valve V13,preferably a solenoid valve, arranged between the external circuit ofthe thermal user plant 10 and the external circuit of the thermal userplant 13. The external three-way valve V13, together with the alreadydescribed three-way valve V11 of the heat pump unit 1, allows line FL1to be connected to the external circuit of the thermal user plant 13bypassing the external circuit of the thermal user plant 10.

In particular, in the cooling operating configuration shown in FIG. 9B,the three-way valve V11 connects line FL1 to the external circuit of thethermal user plant 13 whereas the external three-way valve V13 allowsthe external circuit of the thermal user plant 10 to be bypassed.Thereby, the heat power released by the main condenser S4 (and by thesecondary condenser S1 when the secondary circuit 3 is active, acondition which may also occur during the cooling operation to meet ahigh hot water requirement) can be used for producing high temperaturesanitary hot water rather than dispersing such a power at the heat sink20. This operating mode requires circuit FL1 to be a closed circuit.

FIGS. 10A and 10B show a ninth preferred embodiment of the heat pumpunit 1 which differs from that of FIGS. 9A and 9B mainly in that itcomprises a further heat exchanger S3 in the first sub-circuit 2 a forperforming the higher temperature main heat pump cycle HPCM_HT.

In particular, the heat exchanger S3 is connected downstream of thefirst sub-circuit 2 a so as to be downstream of the main condenser S4and upstream of the heat exchanger device S2 and of the heat exchangerS5 and is adapted, as the latter, to perform an undercooling of theoperating fluid of the higher temperature main heat pump cycle HPCM_HTafter the condensation of the same in the main condenser S4.

The heat exchanger S3 is further selectively connectable in line FL1 forthe connection to the external circuit of the thermal user plant 10, inwhich the main condenser S4 and the secondary condenser S1 are alsoconnected. This is preferably obtained by means of a three-way valveV10, preferably a modulating solenoid valve, arranged in line FL1 so asto allow the connection in such a line alternately of the heat exchangerS3 or of the secondary condenser S1.

The heat exchanger S3, in the heating operating configuration (FIG. 10A)allows the use of the heat power resulting from an undercooling of theoperating fluid of the higher temperature main heat pump cycle HPCM_HTfor preheating the heat carrier fluid of the first thermal user plant 10before it reaches the main condenser S4. As explained above, this leadsto a significant improvement of the overall COP of the heat pump unit 1in particular in operating conditions in which a decrease in thetemperature level of the thermal user plant 10 is acceptable, the heatpower transferred thereto being equal, as it may happen for example in ahigh temperature heating plant in spring and autumn.

Therefore, with reference to the heating operating configuration (FIG.10A) of the ninth embodiment described above, in operating conditions inwhich the temperature level in the thermal user plant 10 must be maximum(for example in full winter), the three-way valve V10 is preferablydiverted so as to connect the secondary condenser S1 in line FL1 andexclude the heat exchanger S3. Advantageously, the heat power providedby the undercooling of the operating fluid of the higher temperaturemain heat pump cycle HPCM_HT can thus be transferred to the thermal userplant 10 at a higher temperature, due to the secondary heat pump cycleHPCS performed in the secondary circuit 3 (active compressor C3), asalready described with reference to the above embodiments. In operatingconditions in which the temperature level in the thermal user plant 10may be reduced, the backflow of heat carrier fluid from the thermal userplant is partly or totally diverted towards the heat exchanger S3through the three-way valve V10. In case of partial diversion, thesecondary circuit 3 may be deactivated or not (compressor C3 cut off oroff), whereas in case of full diversion, the secondary circuit 3 isdeactivated (compressor C3 off). In case of full diversion towards theheat exchanger S3, the heat power available from the undercooling of theoperating fluid of the higher temperature main heat pump cycle HPCM_HTis transferred to the thermal user plant 10 directly, without heatincrease, through the heat exchanger S3. The adjustment of the deliverytemperature for the thermal user plant 10 takes place through themodulation of the three-way valve V10. A further advantage may beobtained by shutting or reducing the number of revolutions ofcompressors C1 and C2 in order to reduce the heat power delivered.

In the heating operating configuration shown in FIG. 10A, the use levelof the heat exchanger S5, i.e. the fraction of undercooling heat powerused therein with respect to the total available, depends on thecorresponding use level of the heat exchanger device S2 and of heatexchanger S3.

In particular, the use level of heat exchanger S5 is maximum when thethree-way valve V10 is diverted so as to exclude the heat exchanger S3and the secondary circuit 3 is not active (compressor C3 off). On thecontrary, the use level is null when all the undercooling heat power isused in the heat exchanger device S2 (for example in full winteroperating conditions) or in heat exchanger S3 (for example in autumn andspring operating conditions). In this case, the heat exchanger S5 isexcluded from line FL1 by closing valve V7. In intermediate situations,the use level of the heat exchanger S5 is partial and valve V7 mustmodulate accordingly. In the cooling operating configuration (FIG. 10B)of the ninth preferred embodiment of the heat pump unit 1, the use ofthe heat exchanger S3 is not generally required and the three-way valveV10 is therefore diverted so as to exclude such a heat exchanger fromline FL1.

In all the embodiments described, the heat pump unit 1 preferablycomprises also a programmable control unit not shown in the figures. Inparticular, such a control unit may be suitably programmed forcontrolling the opening/closing, the modulation or diverting of thevalves as well as the switching on/off, the shutting degree or thenumber of revolutions of the compressors present in each embodiment ofthe heat pump unit 1.

The operating fluids used in the various heat pump cycles performed inthe heat pump unit 1 may be equal to or different from, each other.

Operating fluids are preferably selected that allow the followingadvantageous features to be combined for the operation of the heat pumpunit 1:

-   -   limit curves, and in particular lower limit curve, in diagrams        h-p highly inclined in the direction of the increasing        enthalpies;    -   high specific heat of the operating fluid at the liquid state        with respect to the latent condensation/evaporation heat;    -   high specific heat of the operating fluid at the vapor state        with respect to the latent condensation/evaporation heat.

The first two features mentioned above are particularly important forembodiments or operating conditions that use strong undercooling whereasthe third one is particularly important for all the embodiments oroperating conditions that use strong overheating.

In particular, in order to obtain the best performance of the heat pumpunit 1, the following operating fluids have proven to be particularlyadvantageous: (E)-2-butene, (Z)-2-butene, 1-butylene, dimethyl ketone,methylacetylene, methyl alcohol, methylpentane, methylpropene, n-hexane,R1270, R290, R600, R600a, R601, R601a, RE-170, tetramethylmethane orRC-270.

Besides having at least one or more of the desired features listedabove, these operating fluids have the advantage of being so-called“natural” cooling fluids, i.e. not harmful for the environment from theviewpoint of negative effects on the stratospheric ozone, or from theviewpoint of the greenhouse effect.

If the type of operating fluid selected, in particular for itshydrocarbon nature, poses safety issues (fire hazard) in the cases inwhich the heat pump unit 1 must be installed in underground or basementrooms, the latter is preferably provided also with means for thedetection and evacuation of gas leaks.

FIG. 11 shows an embodiment of the heat pump unit 1 comprising a systemfor the detection and evacuation of gas leaks. By way of example, theconfiguration of the heat pump unit 1 shown corresponds to the firstembodiment described above with reference to FIG. 1.

The system for the detection and evacuation of gas comprises at leastone gas detector 31, positioned as close as possible to the bottom ofthe heat pump unit 1 and ventilation means 32, which can be activated bythe gas detector 31 and arranged so that the suction thereof is alsoclose to the bottom of the heat pump unit 1, whereas the deliverythereof is connected to a gas evacuation conduit in communication withthe external environment. Optionally, there may be provided a dedicatedcontrol device 34 adapted to receive signals from the gas detector 31and to control the ventilation means 32 accordingly. The control device34 may also control sound and/or light warning means 35, if provided,and/or be configured for sending alarm signals to an optional externalmonitoring/supervision system (not shown). The functions of the controldevice 34 may also be carried out by the programmable control unit ofthe heat pump unit 1.

A man skilled in the art may obviously use the technical features of theheat pump unit 1 of the invention disclosed with reference to thepreferred embodiments described above also in different combinations inorder to meet specific and contingent application requirements.

Numerical simulations were carried out in order to determine theimprovement in the energy efficiency that may be obtained with the heatpump unit 1 as compared to a heat pump unit of the prior art withsimilar configuration.

Table 1 shows the comparative results of simulations related to asingle-stage configuration, in the case of the invention correspondingto the first preferred embodiment described above with reference toFIGS. 1 and 1A.

TABLE 1 Single-stage heat pump unit Invention Prior art HPCM useful heatpower [kW] 100 138.1 mass flow rate [kg/s] 0.337 0.466 h [kJ/kg] Tin [°C.] Tout [° C.] h [kJ/kg] Tin [° C.] Tout [° C.] evaporation + 347.540.0 45.0 247.7 40 45 overheating (S8) compression (C2) 48.9 45.0 81.848.9 45 81.8 de-overheating + 296.6 81.8 80.0 296.6 81.8 80 condensation(S4) undercooling (S2) 99.9 80.0 43.0 — — — HPCS useful heat power [kW]38.1 — mass flow rate [kg/s] 0.101 — evaporation + 334 40.0 79.0 — — —overheating (S2) compression (C3) 44 79.0 107 — — — de-overheating + 378107 73.0 — — — condensation (S1) Overall cycle useful heat power [kW]138.1 138.1 electrical power [kW] 20.9 22.8 COP 6.61 6.07

Table 2 shows the comparative results of simulations related to atwo-stage configuration, in the case of the invention corresponding tothe second preferred embodiment described above with reference to FIGS.2 and 2A.

The tables show, for each heat pump cycle performed in the specific heatpump unit (HPCM, i.e. HPCM_HT and HPCM_LT, HPCMS), the useful heatpower, the mass flow rate and, for each cycle transformation, thespecific enthalpy variation (h) and the operating fluid temperatures atthe beginning (Tin) and at the end (Tout) of the transformation.Finally, the overall useful heat power, the electrical power and the COPof the heat pump unit considered are shown (overall cycle). Withreference to the circuit diagram of FIGS. 1 and 2, for eachtransformation, the component at which it is performed is also shown inbrackets.

TABLE 2 Two-stage heat pump unit Invention Prior art HPCM_LT heat power[kW] 118.1 114.0 mass flow rate [kg/s] 0.339 0.331 h [kJ/kg] Tin [° C.]Tout [° C.] h [kJ/kg] Tin [° C.] Tout [° C.] evaporation + 293.2 10.015.0 285.4 10.0 15.0 overheating (S8) compression (C1) 55.2 15.0 52.559.1 15.0 55.3 de-overheating + 348.5 52.5 47.0 344.5 55.3 50.0condensation (S7) HPCM_HT useful heat power [kW] 100.0 136.4 mass flowrate [kg/s] 0.337 0.460 evaporation + 350.8 44.0 49.0 247.7 40 45overheating (S7) compression (C2) 43.6 49.0 82.0 48.9 45 81.8de-overheating + 297.1 82.0 80.0 296.6 81.8 80 condensation (S4)undercooling (S2) 97.3 80.0 44.0 — — — HPCS useful heat power [kW] 36.4— mass flow rate [kg/s] 0.098 — evaporation + 333 44.0 79.0 — — —overheating (S2) compression (C3) 38 79.0 104.9 — — — de-overheating +370 104.9 73.0 — — — condensation (S1) Overall cycle useful heat power136.4 136.4 electrical power 37.1 42.0 COP 3.68 3.25

R600 has been considered as operating fluid. In the configurations whichprovide for multiple heat pump cycles, the operating fluid was the samefor all cycles.

The simulations were carried out with the same useful heat power of theheat pump unit (overall cycle), equal to 138.1 kW in the simulationsrelated to single-stage configurations and to 136.4 kW in thesimulations related to two-stage configurations, respectively.

As it may be seen, the COP of the heat pump units of the invention ishigher than that of the heat pump unit of the prior art having similarconfiguration. In particular, there occurs an increase of about 9% inthe COP for a single-stage configuration, and of about 13% for atwo-stage configuration.

Moreover, it is noted that in the case of the heat pump units of theinvention, the mass flow rates of operating fluid in the secondary heatpump cycles HPCS are substantially lower than the mass flow rates ofoperating fluid in the main heat pump cycles HPCM, i.e. HPCM_HT andHPCM_HT. In particular, the ratio between the above flow rates is about1:3. As already explained above, the possibility of performing thesecondary heat pump cycles HPCS with minimum mass flow rates ofoperating fluid is one of the main factors to which the improvement inthe COP which can be obtained with the heat pump units of the inventioncan be ascribed.

1. Heat pump unit comprising at least one main circuit adapted toperform a main heat pump cycle with a respective operating fluid, saidat least one main circuit comprising: a main condenser adapted toperform the condensation of the operating fluid of said main heat pumpcycle and intended to be connected to an external circuit of a firstthermal user plant in a heating operating mode of said heat pump unit; afirst heat exchanger, connected downstream of said main condenser andupstream of the expansion means of said at least one main circuit,adapted to perform an undercooling of the operating fluid of said mainheat pump cycle after the condensation of the same in said maincondenser, and a main evaporator adapted to perform the evaporation ofthe operating fluid of said main heat pump cycle and intended to beconnected to an external circuit of a heat sink in a heating operatingmode of said heat pump unit, characterized by comprising a secondarycircuit adapted to perform a secondary heat pump cycle with a respectiveoperating fluid, said secondary circuit comprising: a secondaryevaporator adapted to perform at least the evaporation of the operatingfluid of said secondary heat pump cycle and in heat exchangerelationship with said first heat exchanger to transfer heat powerreleased by the operating fluid of said main heat pump cycle during saidundercooling to the operating fluid of said secondary heat pump cycle,and a secondary condenser adapted to perform the condensation of theoperating fluid of said secondary heat pump cycle and intended to beconnected to the external circuit of said first thermal user plant or toan external circuit of a second thermal user plant, different from saidfirst thermal user plant.
 2. Heat pump unit according to claim 1,wherein both said main condenser (S4) and said secondary condenser areintended to be connected to the external circuit of said first thermaluser plant and are connected to each other so as to be in series in saidexternal circuit of said first thermal user plant.
 3. Heat pump unitaccording to claim 1, wherein said main circuit comprises a firstsub-circuit adapted to perform a higher temperature main heat pump cyclewith a respective operating fluid and a second sub-circuit adapted toperform a lower temperature main heat pump cycle with a respectiveoperating fluid, wherein said first and second sub-circuits are incascading heat exchange relationship with each other in order to performglobally a two-stage main heat pump cycle, and wherein said maincondenser and said first heat exchanger are connected in said firstsub-circuit and said main evaporator is connected in said secondsub-circuit.
 4. Heat pump unit according to claim 3, wherein said firstsub-circuit comprises a second heat exchanger connected downstream ofsaid first heat exchanger and upstream of expansion means of said firstsub-circuit said second heat exchanger being adapted to perform anundercooling of the operating fluid of said higher temperature main heatpump cycle after the condensation thereof and being selectivelyconnectable to the external circuit of said heat sink in order toperform a preheating of a heat carrier fluid coming from said heat sinkby means of heat power released during said undercooling by theoperating fluid of said higher temperature main heat pump cycle.
 5. Heatpump unit according to claim 4, wherein said second heat exchanger isfurther selectively connected to an external circuit of a third thermaluser plant.
 6. Heat pump unit according to claim 4, wherein said secondsub-circuit comprises a third heat exchanger connected downstream of acondenser and upstream of expansion means of said second sub-circuit,said third heat exchanger being adapted to perform an undercooling ofthe operating fluid of said lower temperature main heat pump cycle afterthe condensation thereof and being selectively connectable to theexternal circuit of said heat sink so as to perform, preferablyindependently with respect to said second heat exchanger, a preheatingof a heat carrier fluid coming from said heat sink by means of heatpower released during said undercooling by the operating fluid of saidlower temperature main heat pump cycle.
 7. Heat pump unit according toclaim 6, wherein said third heat exchanger is further selectivelyconnectable to the external circuit of said third thermal user plant. 8.Heat pump unit according to claim 3, wherein said first sub-circuitcomprises a fourth heat exchanger connected downstream of said maincondenser and upstream of said first heat exchanger, said fourth heatexchanger being adapted to perform an undercooling of the operatingfluid of said higher temperature main heat pump cycle after thecondensation of the same and being selectively connectable to theexternal circuit of said first thermal user plant so as to be in serieswith said main condenser in said external circuit of said first userplant.
 9. Heat pump unit according to claim 1, comprising switchingmeans adapted to allow an exchange of connections of the externalcircuits of at least said first thermal user plant and said heat sinkrespectively with at least said main condenser and with said mainevaporator.
 10. Heat pump according to claim 1, wherein the operatingfluid of said main heat pump cycle, or the operating fluids of saidhigher temperature main heat pump cycle and said lower temperature mainheat pump cycle respectively, and the operating fluid of said secondaryheat pump cycle are selected from the group consisting of: (E)-2-butene,(Z)-2-butene, 1-butylene, dimethyl ketone, methylacetylene, methylalcohol, methylpentane, methylpropene, n-hexane, R1270, 8290, R600,R600a, R601, R601a, RE-170, tetramethylmethane or RC-270.
 11. Heat pumpunit according to claim 1, comprising means for detecting and evacuatinggas leaks.
 12. System for heating/cooling environments and/or forproducing sanitary hot water comprising a heat pump unit according toclaim
 1. 13. Heat pump unit according to claim 5, wherein said secondsub-circuit comprises a third heat exchanger connected downstream of acondenser and upstream of expansion means of said second sub-circuit,said third heat exchanger being adapted to perform an under-cooling ofthe operating fluid of said lower temperature main heat pump cycle afterthe condensation thereof and being selectively connectable to theexternal circuit of said heat sink so as to perform, preferablyindependently with respect to said second heat exchanger, a preheatingof a heat carrier fluid coming from said heat sink by means of heatpower released during said undercooling by the operating fluid of saidlower temperature main heat pump cycle.
 14. Heat pump unit according toclaim 7, wherein said third heat exchanger is further selectivelyconnectable to the external circuit of said third thermal user plant.